Taxonomy, biology, and periodontal aspects of Fusobacterium nucleatum

Activated zeolite--suitable carriers for microorganisms in anaerobic digestion processes?

Plant cell wall structures represent a barrier in the biodegradation process to produce biogas for combustion and energy production. Consequently, approaches concerning a more efficient de-polymerisation of cellulose and hemicellulose to monomeric sugars are required. Here, we show that natural activated zeolites (i.e. trace metal activated zeolites) represent eminently suitable mineral microhabitats and potential carriers for immobilisation of microorganisms responsible for anaerobic hydrolysis of biopolymers stabilising related bacterial and methanogenic communities. A strategy for comprehensive analysis of immobilised anaerobic populations was developed that includes the visualisation of biofilm formation via scanning electron microscopy and confocal laser scanning microscopy, community and fingerprint analysis as well as enzyme activity and identification analyses. Using SDS polyacrylamide gel electrophoresis, hydrolytical active protein bands were traced by congo red staining. Liquid chromatography/mass spectroscopy revealed cellulolytical endo- and exoglucanase (exocellobiohydrolase) as well as hemicellulolytical xylanase/mannase after proteolytic digestion. Relations to hydrolytic/fermentative zeolite colonisers were obtained by using single-strand conformation polymorphism analysis (SSCP) based on amplification of bacterial and archaeal 16S rRNA fragments. Thereby, dominant colonisers were affiliated to the genera Clostridium, Pseudomonas and Methanoculleus. The specific immobilisation on natural zeolites with functional microbes already colonising naturally during the fermentation offers a strategy to systematically supply the biogas formation process responsive to population dynamics and process requirements.

The surface layer of Tannerella forsythia contributes to serum resistance and oral bacterial coaggregation

Tannerella forsythia is an anaerobic, Gram-negative bacterium involved in the so-called "red complex," which is associated with severe and chronic periodontitis. The surface layer (S-layer) of T. forsythia is composed of cell surface glycoproteins, such as TfsA and TfsB, and is known to play a role in adhesion/invasion and suppression of proinflammatory cytokine expression. Here we investigated the association of this S-layer with serum resistance and coaggregation with other oral bacteria. The growth of the S-layer-deficient mutant in a bacterial medium containing more than 20% non-heat-inactivated calf serum (CS) or more than 40% non-heat-inactivated human serum was significantly suppressed relative to that of the wild type (WT). Next, we used confocal microscopy to perform quantitative analysis on the effect of serum. The survival ratio of the mutant exposed to 100% non-heat-inactivated CS (76% survival) was significantly lower than that of the WT (97% survival). Furthermore, significant C3b deposition was observed in the mutant but not in the WT. In a coaggregation assay, the mutant showed reduced coaggregation with Streptococcus sanguinis, Streptococcus salivarius, and Porphyromonas gingivalis but strong coaggregation with Fusobacterium nucleatum. These results indicated that the S-layer of T. forsythia plays multiple roles in virulence and may be associated with periodontitis.

The relationship between turbidity of mouth-rinsed water and oral health status

OBJECTIVES

The purpose of this study was to examine the relationship between turbidity of mouth rinsed water and oral health status such as dental and periodontal conditions, oral hygiene status, flow rate of saliva and oral bacteria.

MATERIALS AND METHODS

Subjects were 165 patients who visited the Dental Hospital, Tokyo Medical and Dental University. Oral health status, including dental and periodontal conditions, oral hygiene status and flow rate of saliva, was clinically examined. The turbidity was measured with a turbidimeter. Quantification of Fusobacterium spp, Porphyromonas gingivalis, Tannerella forsythia, Treponema denticola and total bacteria levels was performed using real-time PCR. The Pearson correlation and multiple regression analysis were used to explore the associations between the turbidity and oral health parameters.

RESULTS

The turbidity showed significant correlations with the number of decayed teeth and deep pockets, the plaque index, extent of tongue coating and Fusobacterium spp, P. gingivalis, T. forsythia, T. denticola and total bacteria levels. In a multiple regression model, the turbidity was negatively associated with the flow rate of saliva and positively associated with the total number of bacteria (p < 0.001).

CONCLUSION

Current findings suggested that turbidity of mouth rinsed water could be used as an indicator to evaluate oral health condition and the amount of bacteria in the oral cavity. In addition, the turbiditimeter appeared as a simple and objective device for screening abnormality of oral health condition at chair side as well as community-based research.

Maternal oral origin of Fusobacterium nucleatum in adverse pregnancy outcomes as determined using the 16S-23S rRNA gene intergenic transcribed spacer region

Fusobacterium nucleatum, a common Gram-negative anaerobe prevalent in the oral cavity, possesses the ability to colonize the amniotic cavity and the fetus. However, F. nucleatum may also be part of the vaginal microbiota from where it could reach the amniotic tissues. Due to the heterogeneity of F. nucleatum, consisting of five subspecies, analysis at the subspecies/strain level is desirable to determine its precise origin. The aims of this study were: (i) to evaluate the use of the 16S-23S rRNA gene intergenic transcribed spacer (ITS) region as a tool to differentiate subspecies of F. nucleatum, and (ii) to design a simplified technique based on the ITS to determine the origin of F. nucleatum strains associated with adverse pregnancy outcomes. Amplified fragments of the 16S-23S rRNA gene ITS region corresponding to the five subspecies of F. nucleatum were subjected to cloning and sequencing to characterize the different ribosomal operons of the subspecies. Distinctive length and sequence patterns with potential to be used for identification of the subspecies/strain were identified. These were used to evaluate the origin of F. nucleatum identified in neonatal gastric aspirates (swallowed amniotic fluid) by sequence comparisons with the respective oral and vaginal maternal samples. A simplified technique using a strain-specific primer in a more sensitive nested PCR was subsequently developed to analyse ten paired neonatal-maternal samples. Analysing the variable fragment of the ITS region allowed the identification of F. nucleatum subsp. polymorphum from an oral origin as potentially being involved in neonatal infections. Using a strain-specific primer, the F. nucleatum subsp. polymorphum strain was detected in both neonatal gastric aspirates and maternal oral samples in cases of preterm birth from mothers presenting with localized periodontal pockets. Interestingly, the same strain was not present in the vaginal sample of any case investigated. The 16S-23S rRNA gene ITS can be a useful tool to determine the origin of F. nucleatum. The results of this study strongly indicate that F. nucleatum subsp. polymorphum of oral origin could be involved with pregnancy complications.

A proteomic investigation of Fusobacterium nucleatum alkaline-induced biofilms

Background

The Gram negative anaerobe Fusobacterium nucleatum has been implicated in the aetiology of periodontal diseases. Although frequently isolated from healthy dental plaque, its numbers and proportion increase in plaque associated with disease. One of the significant physico-chemical changes in the diseased gingival sulcus is increased environmental pH. When grown under controlled conditions in our laboratory, F. nucleatum subspecies polymorphum formed mono-culture biofilms when cultured at pH 8.2. Biofilm formation is a survival strategy for bacteria, often associated with altered physiology and increased virulence. A proteomic approach was used to understand the phenotypic changes in F. nucleatum cells associated with alkaline induced biofilms. The proteomic based identification of significantly altered proteins was verified where possible using additional methods including quantitative real-time PCR (qRT-PCR), enzyme assay, acidic end-product analysis, intracellular polyglucose assay and Western blotting.

Results

Of 421 proteins detected on two-dimensional electrophoresis gels, spot densities of 54 proteins varied significantly (p < 0.05) in F. nucleatum cultured at pH 8.2 compared to growth at pH 7.4. Proteins that were differentially produced in biofilm cells were associated with the functional classes; metabolic enzymes, transport, stress response and hypothetical proteins. Our results suggest that biofilm cells were more metabolically efficient than planktonic cells as changes to amino acid and glucose metabolism generated additional energy needed for survival in a sub-optimal environment. The intracellular concentration of stress response proteins including heat shock protein GroEL and recombinational protein RecA increased markedly in the alkaline environment. A significant finding was the increased abundance of an adhesin, Fusobacterial outer membrane protein A (FomA). This surface protein is known for its capacity to bind to a vast number of bacterial species and human epithelial cells and its increased abundance was associated with biofilm formation.

Conclusion

This investigation identified a number of proteins that were significantly altered by F. nucleatum in response to alkaline conditions similar to those reported in diseased periodontal pockets. The results provide insight into the adaptive mechanisms used by F. nucleatum biofilms in response to pH increase in the host environment.

T-RFLP-based differences in oral microbial communities as risk factor for development of oral diseases under stress

The human oral microbiome is comprised of approximately 800 different bacterial species many of which are as yet uncultivated. Their dynamics and variability in relation to health and disease are still poorly understood. Here we tested the hypothesis that the emergence of stress-induced periodontal diseases is predictable based on the composition of the initial microbiota. As a model, we analysed 58 individuals performing a challenging expedition (exposure to various stress-factors due to changes in diet, hygiene, temperature, physical and mental stress) in remote regions of the Himalayans (Annapurna Himal). Plaque samples were taken at start (Bhulbule) and destination (3000 meter difference in altitude) seven days later (Manang). Twenty-eight individuals remained symptom-free (Group I) while 30 participants developed periodontal problems, mostly gingivitis (Group II). The microbiota was monitored via T-RFLP-analysis of amplified 16S rRNA genes directly from the plaque samples. Based on the Additive-Main-Effects-Multiplicative-Interactions-model (AMMI) using the T-Rex software variation from T-RF main effects was at least 95%, indicating that most variation was due to inherent differences in microbial communities among individuals. However, an interaction signal up to 3% was consistently observed between groups I and II but not between the two time points of sampling regardless of selected analytical parameters. The data, supported by heterogeneity, diversity and similarity indices indicated marked differences between groups I and II already prior the onset of clinical symptoms. These differences may provide the basis for using ecological parameters of oral microbial communities as early diagnostic marker for the onset of oral disorders and infections.

Fusobacterium nucleatum infection mimicking metastatic cancer

A 48-year-old man presented with fevers, chills, weight loss, multiple liver masses, and several superficial and deep venous thromboses in lower extremities. Cancer work up was negative. A liver biopsy grew Fusobacterium nucleatum. To our knowledge, F. nucleatum infection presenting with multiple liver masses and Trousseau-like syndrome has not been reported earlier.

The FomA porin from Fusobacterium nucleatum is a Toll-like receptor 2 agonist with immune adjuvant activity

Many bacterial components selectively activate immune and nonhematopoietic target cells via Toll-like receptor (TLR) signaling; modulation of such host responses defines the immune adjuvant properties of these bacterial products. For example, the outer membrane protein porins from Neisseria, Salmonella, and Shigella are known TLR2 agonists with established systemic and mucosal immune adjuvanticity. Early work indicated that the FomA porin from Fusobacterium nucleatum has immune adjuvant activity in mice. Using a purified recombinant FomA, we have verified its immune stimulatory properties and have defined a role for TLR2 signaling in its in vitro and in vivo activity. FomA induces interleukin 8 (IL-8) secretion and NF-κB-dependent luciferase activity in HEK cells expressing TLR2, IL-6 secretion, and cell surface upregulation of CD86 and major histocompatibility complex (MHC) II in primary B cells from wild-type mice, but it fails to activate cells from TLR2 knockout mice. Accordingly, the immune adjuvant activity of FomA is also TLR2 dependent. In a mouse model of immunization with ovalbumin (OVA), FomA induces enhanced production of OVA-specific IgM and IgG, including IgG1 and IgG2b antibodies, as well as enhanced secretion of IL-10 and IL-6, consistent with a Th2-type adjuvant effect. We also observe a moderate production of anti-FomA antibodies, suggesting that FomA is also immunogenic, a quality that is also TLR2 dependent. Therefore, modulation of host immune responses by FomA may be effective for targeting general host immunity not only to pathogens (as a novel TLR2 adjuvant) but also to F. nucleatum itself (as an antigen), expanding its use as a self-adjuvanted antigen in an immunization strategy against polymicrobial infections, including those by F. nucleatum.

The role of coaggregation between Porphyromonas gingivalis and Fusobacterium nucleatum on the host response to mixed infection

AIM

To evaluate the role of coaggregation between Porphyromonas gingivalis and Fusobacterium nucleatum on the virulence of the mixed infection in mice.

MATERIALS AND METHODS

Inhibition of coaggregation was carried out using lactose. In vitro, inhibition of coaggregation was verified using a coaggregation assay. In vivo, the virulence of the mixed infection, with and without coaggregation, was examined in a model of experimental periodontitis in mice. The local host response to the mixed infection, with or without coaggregation, was examined using the subcutaneous chamber model of infection.

RESULTS

Lactose inhibited the coaggregation between P. gingivalis and F. nucleatum at all the tested concentrations (1-0.0625 M). Surprisingly, the addition of lactose to the mixed infection increased the severity of experimental periodontitis (as measured by alveolar bone loss) compared with mixed infection with coaggregating bacteria. The addition of lactose to the mixed infection resulted in mild attenuation of TNFα and IL-1β levels. In addition, inhibition of coaggregation resulted in inhibition of the phagocytosis of F. nucleatum and augmentation of the phagocytosis of P. gingivalis.

CONCLUSIONS

The ability of P. gingivalis and F. nucleatum to coaggregate may limit their ability to induce experimental periodontitis in a mixed infection model. Moreover, there is a shift in the phagocytosis pattern of the bacteria with the annulment of coaggregeaiton, with a reduction in F. nucleatum phagocytosis and amplification of P. gingivalis phagocytosis. The increased virulence of the mixed infection without coaggregation may surprisingly lay in the sustention of F. nucleatum in the infected sites.

Fusobacterium nucleatum and Tannerella forsythia induce synergistic alveolar bone loss in a mouse periodontitis model

Tannerella forsythia is strongly associated with chronic periodontitis, an inflammatory disease of the tooth-supporting tissues, leading to tooth loss. Fusobacterium nucleatum, an opportunistic pathogen, is thought to promote dental plaque formation by serving as a bridge bacterium between early- and late-colonizing species of the oral cavity. Previous studies have shown that F. nucleatum species synergize with T. forsythia during biofilm formation and pathogenesis. In the present study, we showed that coinfection of F. nucleatum and T. forsythia is more potent than infection with either species alone in inducing NF-κB activity and proinflammatory cytokine secretion in monocytic cells and primary murine macrophages. Moreover, in a murine model of periodontitis, mixed infection with the two species induces synergistic alveolar bone loss, characterized by bone loss which is greater than the additive alveolar bone losses induced by each species alone. Further, in comparison to the single-species infection, mixed infection caused significantly increased inflammatory cell infiltration in the gingivae and osteoclastic activity in the jaw bones. These data show that F. nucleatum subspecies and T. forsythia synergistically stimulate the host immune response and induce alveolar bone loss in a murine experimental periodontitis model.

Sialic acid, periodontal pathogens and Tannerella forsythia: stick around and enjoy the feast!

Periodontal pathogens, like any other human commensal or pathogenic bacterium, must possess both the ability to acquire the necessary growth factors and the means to adhere to surfaces or reside and survive in their environmental niche. Recent evidence has suggested that sialic acid containing host molecules may provide both of these requirements in vivo for several periodontal pathogens but most notably for the red complex organism Tannerella forsythia. Several other periodontal pathogens also possess sialic acid scavenging enzymes - sialidases, which can also expose adhesive epitopes, but might also act as adhesins in their own right. In addition, recent experimental work coupled with the release of several genome sequences has revealed that periodontal bacteria have a range of sialic acid uptake and utilization systems while others may also use sialic acid as a cloaking device on their surface to mimic host and avoid immune recognition. This review will focus on these systems in a range of periodontal bacteria with a focus on Ta. forsythia.

Fusobacterium nucleatum infection is prevalent in human colorectal carcinoma

An estimated 15% or more of the cancer burden worldwide is attributable to known infectious agents. We screened colorectal carcinoma and matched normal tissue specimens using RNA-seq followed by host sequence subtraction and found marked over-representation of Fusobacterium nucleatum sequences in tumors relative to control specimens. F. nucleatum is an invasive anaerobe that has been linked previously to periodontitis and appendicitis, but not to cancer. Fusobacteria are rare constituents of the fecal microbiota, but have been cultured previously from biopsies of inflamed gut mucosa. We obtained a Fusobacterium isolate from a frozen tumor specimen; this showed highest sequence similarity to a known gut mucosa isolate and was confirmed to be invasive. We verified overabundance of Fusobacterium sequences in tumor versus matched normal control tissue by quantitative PCR analysis from a total of 99 subjects (p = 2.5 × 10(-6)), and we observed a positive association with lymph node metastasis.

Fusobacterium nucleatum prosthetic hip infection in an adult with sickle cell-beta thalassemia

Fusobacterium nucleatum is an anaerobic Gram-negative bacillus commensal to the human oropharynx and gastrointestinal tract which causes an array of human infection, yet it has never been associated with infection of prosthetic joints. We report the first case of prosthetic hip infection caused by F. nucleatum in a man with sickle cell-beta thalassemia.

Characteristics and outcomes of Fusobacterium nucleatum bacteremia--a 6-year experience at a tertiary care hospital in northern Taiwan

Fusobacterium nucleatum bacteremia is critical and not well defined. To identify the clinical characteristics and outcomes, we conducted a retrospective review of hospitalized patients from January 2004 to December 2009 at a tertiary center in northern Taiwan. Fifty-seven patients were enrolled. The mean age was 58.1 years, and the mean Pitt bacteremia score was 4.7. Males predominated (59.6%), and the overall 30-day mortality rate was up to 47.4%. Malignancy was the major comorbidity (26/57, 45.6%), especially oropharyngeal and gastrointestinal cancers (19/26, 73.1%). Pneumonia (17/57, 29.8%) was the most common presentation with high rates of respiratory failure (15/17, 88.2%) and mortality (11/17, 64.7%), followed by intra-abdominal infections (7/57, 12.3%). In multivariate analysis, higher Pitt bacteremia score, nosocomial infection, anemia, and intensive care unit stay were the independent factors for 30-day mortality. Nosocomial F. nucleatum bacteremia was a significant mortality predictor independent to other parameters of disease severities.

Oxidative stress response in the opportunistic oral pathogen Fusobacterium nucleatum

The anaerobic, Gram-negative bacillus Fusobacterium nucleatum plays a vital role in oral biofilm formation and the development of periodontal disease. The organism plays a central bridging role between early and late colonizers within dental plaque and plays a protective role against reactive oxygen species. Using a two-dimensional gel electrophoresis and mass spectrometry approach, we have annotated 78 proteins within the proteome of F. nucleatum subsp. nucleatum and identified those proteins whose apparent intracellular concentrations change in response to either O(2)- or H(2)O(2)-induced oxidative stress. Three major protein systems were altered in response to oxidative stress: (i) proteins of the alkyl hydroperoxide reductase/thioredoxin reductase system were increased in intracellular concentration; (ii) glycolytic enzymes were modified by oxidation (i.e. D-glyceraldehyde 3-phosphate dehydrogenase, and fructose 6-phosphate aldolase) or increased in intracellular concentration, with an accompanying decrease in ATP production; and (iii) the intracellular concentrations of molecular chaperone proteins and related proteins (i.e. ClpB, DnaK, HtpG, and HrcA) were increased.

Glutamate racemization and catabolism in Fusobacterium varium

The pathways of glutamate catabolism in the anaerobic bacterium Fusobacterium varium, grown on complex, undefined medium and chemically defined, minimal medium, were investigated using specifically labelled (13)C-glutamate. The metabolic end-products acetate and butyrate were isolated from culture fluids and derivatized for analysis by nuclear magnetic resonance and mass spectrometry. On complex medium, labels from L-[1-(13)C]glutamate and L-[4-(13)C]glutamate were incorporated into C1 of acetate and equally into C1/C3 of butyrate, while label derived from L-[5-(13)C]glutamate was not incorporated. The isotopic incorporation results and the detection of glutamate mutase and 3-methylaspartate ammonia lyase in cell extracts are most consistent with the methylaspartate pathway, the best known route of glutamate catabolism in Clostridium species. When F. varium was grown on defined medium, label from L-[4-(13)C]glutamate was incorporated mainly into C4 of butyrate, demonstrating a major role for the hydroxyglutarate pathway. Upon addition of coenzyme B(12) or cobalt ion to the defined medium in replicate experiments, isotope was located equally at C1/C3 of butyrate in accord with the methylaspartate pathway. Racemization of D-glutamate and subsequent degradation of L-glutamate via the methylaspartate pathway are supported by incorporation of label into C2 of acetate and equally into C2/C4 of butyrate from D-[3-(13)C]glutamate and the detection of a cofactor-independent glutamate racemase in cell extracts. Together the results demonstrate a major role for the methylaspartate pathway of glutamate catabolism in F. varium and substantial participation of the hydroxyglutarate pathway when coenzyme B(12) is not available.

Predation of oral pathogens by Bdellovibrio bacteriovorus 109J

Periodontal diseases are multifactorial infections elicited by a complex of primarily gram-negative bacteria that interact with host tissues and lead to the destruction of the periodontal structures. Bdellovibrio bacteriovorus is a gram-negative bacterium that preys upon other gram-negative bacteria. It was previously shown that B. bacteriovorus has an ability to attack and remove surface-attached bacteria or biofilms. In this study, we examined the host specificity of B. bacteriovorus strain 109J and its ability to prey on oral pathogens associated with periodontitis, including; Aggregatibacter actinomycetemcomitans, Eikenella corrodens, Fusobacterium nucleatum, Prevotella intermedia, Porphyromonas gingivalis and Tannerella forsythia. We further demonstrated that B. bacteriovorus 109J has an ability to remove biofilms of Ei. corrodens as well as biofilms composed of A. actinomycetemcomitans. Bdellovibrio bacteriovorus was able to remove A. actinomycetemcomitans biofilms developed on hydroxyapatite surfaces and in the presence of saliva, as well as to detach metabolically inactive biofilms. Experiments aimed at enhancing the biofilm removal aptitude of B. bacteriovorus with the aid of extracellular-polymeric-substance-degrading enzymes demonstrated that proteinase-K inhibits predation. However, treating A. actinomycetemcomitans biofilms with DspB, a poly-N-acetylglucosamine (PGA) -hydrolysing enzyme, increased biofilm removal. Increased biofilm removal was also recorded when A. actinomycetemcomitans PGA-defective mutants were used as host cells, suggesting that PGA degradation could enhance the removal of A. actinomycetemcomitans biofilm by B. bacteriovorus.

Isolation of a novel bacteriophage specific for the periodontal pathogen Fusobacterium nucleatum

Fusobacterium nucleatum is a periodontal pathogen that has been directly associated with the development and progression of periodontal disease, a widespread pathology that affects the support tissues of the tooth. We isolated a new bacteriophage (FnpΦ02) that specifically infects this bacterium. Transmission electron microscopy showed that the virion is composed of an icosahedral head and a segmented tail. The size of the phage genome was estimated to be approximately 59 kbp of double-stranded DNA. The morphological features and the genetic characteristics suggest that FnpΦ02 is part of the Siphoviridae family. Using one-step growth and adsorption experiments, the latent period, burst size, and adsorption rate were estimated to be 15 h, 100 infectious units per cell, and 7.5 × 10⁻¹⁰ ml min⁻¹, respectively. A small fragment of phage DNA was cloned and sequenced, showing 93% nucleotide identity with the phage PA6 of Propionibacterium acnes and amino acid identity with fragments of two proteins (Gp3 and Gp4) of this phage. To our knowledge, FnpΦ02 is the first phage described to infect Fusobacterium nucleatum and provides the base for future exploration of phages in the control of periodontal disease.

Fusobacterium nucleatum outer membrane proteins Fap2 and RadD induce cell death in human lymphocytes

Bacterially induced cell death in human lymphocytes is an important virulence factor for pathogenic bacteria. Previously discovered mechanisms of bacterially induced cell death are predominantly based on the transfer of bacterial proteins to the target host cell, such as the toxins secreted through type I, II, and VI secretion systems or effector proteins injected through type III, IV, and Vb secretion systems. Here, we report a mechanism employed by the Gram-negative oral pathogen Fusobacterium nucleatum for cell death induction of human lymphocytes via two outer membrane proteins (OMPs), Fap2 and RadD, which share regions homologous to autotransporter secretion systems (type Va secretion systems). Genetic and physiological studies established that inactivation of the two OMPs led to significantly reduced ability to trigger cell death in Jurkat cells, while the corresponding double mutant was almost completely attenuated. Additional biochemical and molecular analyses demonstrated that cell-free F. nucleatum membranes are sufficient to induce cell death in Jurkat cells, suggesting that no active process or effector protein transfer was necessary to induce eukaryotic cell death.

Production of indole from L-tryptophan and effects of these compounds on biofilm formation by Fusobacterium nucleatum ATCC 25586

The l-tryptophan degradation product indole is a purported extracellular signaling molecule that influences biofilm formation in various bacteria. Here we analyzed the mechanisms of indole production in Fusobacterium nucleatum and the effects of tryptophan and indole on F. nucleatum planktonic and biofilm cells. The amino acid sequence deduced from the fn1943 gene in F. nucleatum ATCC 25586 was 28% identical to that deduced from tnaA in Escherichia coli, which encodes tryptophanase catalyzing the beta-elimination of l-tryptophan to produce indole. The fn1943 gene was cotranscribed with the downstream gene fn1944, which is a homolog of tnaB encoding low-affinity tryptophan permease. The transcript started at position -68 or -153 from the first nucleotide of the fn1943 translation initiation codon. Real-time quantitative PCR showed that much more F. nucleatum fn1943 transcripts were obtained from log-phase cells than from stationary-phase cells. Indole production by the purified recombinant protein encoded by fn1943 was examined using high-performance liquid chromatography. The K(m) and k(cat) of the enzyme were 0.26 +/- 0.03 mM and 0.74 +/- 0.04 s(-1), respectively. F. nucleatum biofilm formation and the biofilm supernatant concentration of indole increased dose dependently with increasing tryptophan concentrations. Exogenous indole also increased F. nucleatum biofilm formation in a dose-dependent manner. Even at very high concentrations, tryptophan did not affect fn1943 expression, whereas similar indole concentrations decreased expression. Thus, exogenous tryptophan and indole were suggested to increase F. nucleatum biofilms.

Novel bisstyryl derivatives of bakuchiol: targeting oral cavity pathogens

Novel bisstyryl derivatives of bakuchiol using Heck coupling reaction as the key step were synthesized and screened against a panel of six oral cavity pathogens for their antimicrobial activity. Four compounds (9-12) showed two to fourfold and four to eightfold better activity (MIC 0.25-16 microg/ml) than bakuchiol and triclosan respectively. These compounds effectively inhibit the biofilm formation of single and multiple species at 2 - 8 x MICs. 4- and 4'-Hydroxy/methoxy styryl moieties of the bakuchiol derivatives play a pivotal role towards the activity as established in the SAR studies. Mechanism of action studies revealed microbial membrane structure disruption as the probable mode of action of these compounds.

Vaccination targeting surface FomA of Fusobacterium nucleatum against bacterial co-aggregation: Implication for treatment of periodontal infection and halitosis

The mechanical therapy with multiple doses of antibiotics is one of modalities for treatment of periodontal diseases. However, treatments using multiple doses of antibiotics carry risks of generating resistant strains and misbalancing the resident body flora. We present an approach via immunization targeting an outer membrane protein FomA of Fusobacterium nucleatum (F. nucleatum), a central bridging organism in the architecture of oral biofilms. Neutralization of FomA considerably abrogated the enhancement of bacterial co-aggregation, biofilms and production of volatile sulfur compounds mediated by an inter-species interaction of F. nucleatum with Porphyromonas gingivalis (P. gingivalis). Vaccination targeting FomA also conferred a protective effect against co-infection-induced gum inflammation. Here, we advance a novel infectious mechanism by which F. nucleatum co-opts P. gingivalis to exacerbate gum infections. FomA is highlighted as a potential target for development of new therapeutics against periodontal infection and halitosis in humans.

Effects of a mouthwash with chlorine dioxide on oral malodor and salivary bacteria: a randomized placebo-controlled 7-day trial

Background

Previous research has shown the oxidizing properties and microbiological efficacies of chlorine dioxide (ClO₂). Its clinical efficacies on oral malodor have been evaluated and reported only in short duration trials, moreover, no clinical studies have investigated its microbiological efficacies on periodontal and malodorous bacteria. Thus, the aim of this study was to assess the inhibitory effects of a mouthwash containing ClO₂ used for 7 days on morning oral malodor and on salivary periodontal and malodorous bacteria.

Methods/Design

A randomized, double blind, crossover, placebo-controlled trial was conducted among 15 healthy male volunteers, who were divided into 2 groups. Subjects were instructed to rinse with the experimental mouthwash containing ClO₂ or the placebo mouthwash, without ClO₂, twice per day for 7 days. After a one week washout period, each group then used the opposite mouthwash for 7 days. At baseline and after 7 days, oral malodor was evaluated with Organoleptic measurement (OM), and analyzed the concentrations of hydrogen sulfide (H₂S), methyl mercaptan (CH₃SH) and dimethyl sulfide ((CH₃)₂S), the main VSCs of human oral malodor, were assessed by gas chromatography (GC). Clinical outcome variables included plaque and gingival indices, and tongue coating index. The samples of saliva were microbiologically investigated. Quantitative and qualitative analyses were performed using the polymerase chain reaction-Invader method.

Results and Discussion

The baseline oral condition in healthy subjects in the 2 groups did not differ significantly. After rinsing with the mouthwash containing ClO₂ for 7 days, morning bad breath decreased as measured by the OM and reduced the concentrations of H₂S, CH₃SH and (CH₃)₂S measured by GC, were found. Moreover ClO₂ mouthwash used over a 7-day period appeared effective in reducing plaque, tongue coating accumulation and the counts of Fusobacterium nucleatum in saliva. Future research is needed to examine long-term effects, as well as effects on periodontal diseases and plaque accumulation in a well-defined sample of halitosis patients and broader population samples.

Trial registration

ClinicalTrials.gov NCT00748943

Autoaggregation response of Fusobacterium nucleatum

Fusobacterium nucleatum is a gram-negative oral bacterial species associated with periodontal disease progression. This species is perhaps best known for its ability to adhere to a vast array of other bacteria and eukaryotic cells. Numerous studies of F. nucleatum have examined various coaggregation partners and inhibitors, but it is largely unknown whether these interactions induce a particular genetic response. We tested coaggregation between F. nucleatum ATCC strain 25586 and various species of Streptococcus in the presence of a semidefined growth medium containing saliva. We found that this condition could support efficient coaggregation but, surprisingly, also stimulated a similar degree of autoaggregation. We further characterized the autoaggregation response, since few reports have examined this in F. nucleatum. After screening several common coaggregation inhibitors, we identified l-lysine as a competitive inhibitor of autoaggregation. We performed a microarray analysis of the planktonic versus autoaggregated cells and found nearly 100 genes that were affected after only about 60 min of aggregation. We tested a subset of these genes via real-time reverse transcription-PCR and confirmed the validity of the microarray results. Some of these genes were also found to be inducible in cell pellets created by centrifugation. Based upon these data, it appears that autoaggregation activates a genetic program that may be utilized for growth in a high cell density environment, such as the oral biofilm.

Mobilization and prevalence of a Fusobacterial plasmid

Fusobacterium nucleatum is a Gram-negative anaerobic rod found in dental plaque biofilms, and is an opportunistic pathogen implicated in periodontitis as well as a wide range of systemic abscesses and infections. Genomic analyses of F. nucleatum indicate considerable genetic diversity and a prominent role for horizontal gene transfer in the evolution of the species. Several plasmids isolated from F. nucleatum, including pFN1, harbor relaxase gene homologs that may function in plasmid mobilization. In this investigation we examined the RP4-mediated mobilization properties of pFN1 and the prevalence of pFN1-related sequences in a panel of F. nucleatum clinical isolates. The fusobacterial plasmid pFN1 was mobilized by RP4 at a high frequency. Deletion analyses were used to delineate the core mobilon of pFN1, which consisted of the relaxase gene (rlx), an upstream open reading frame ORF4 and a region of DNA upstream of ORF4 with potential nic sites. To examine the prevalence of pFN1 in a panel of clinical isolates, total DNA isolated from the strains was hybridized with pFN1 replication (repA) and rlx gene probes. DNA from strains harboring plasmids known to be homologous to pFN1 hybridized with both the repA and rlx probes. Five additional strains were rlx-positive but repA-negative, indicating a greater prevalence of rlx-related genes in comparison with repA-related genes. Plasmid or plasmid-related sequences were identified in 11.5% of the strains examined. These findings demonstrate mobilization properties of a fusobacterial plasmid that may be important in horizontal gene transfer.

Distinctive features of the microbiota associated with different forms of apical periodontitis

Microorganisms infecting the dental root canal system play an unequivocal role as causative agents of apical periodontitis. Although fungi, archaea, and viruses have been found in association with some forms of apical periodontitis, bacteria are the main microbial etiologic agents of this disease. Bacteria colonizing the root canal are usually organized in communities similar to biofilm structures. Culture and molecular biology technologies have demonstrated that the endodontic bacterial communities vary in species richness and abundance depending on the different types of infection and different forms of apical periodontitis. This review paper highlights the distinctive features of the endodontic microbiota associated with diverse clinical conditions.

Characterization of the complex bacterial communities colonizing biliary stents reveals a host-dependent diversity

This study provides a comprehensive survey of the spatial and temporal bacterial composition of biliary stent biofilms. The bacterial diversity, distribution and dynamics of 59 biliary and 4 pancreatic stent communities from 40 patients being treated at two different hospitals, which implant stents either simultaneously or consecutively, were characterized by single-strand conformation polymorphism (SSCP) analysis. Fifty-one phylotypes belonging to 5 bacterial phyla and 24 bacterial families were detected across 63 stents. This is a much broader diversity than previously detected through culture-dependent methods, particularly in regard to the diversity of obligate anaerobes. Stent bacterial diversity was patient-dependent and more similar when stents were implanted simultaneously rather than consecutively. Stent bacterial community composition differed between hospitals specifically because of the difference in abundance of Bifidobacteria. Co-colonization of Veillonella sp., Streptococcus anginosus and organisms closely related to Fusobacterium nucleatum revealed a potentially important attachment and survival strategy that has yet to be reported in biliary stents. This work reveals a more complete survey of the identities of bacterial species that form biofilms in biliary stents, their co-colonization patterns and the natural variation in species composition between different patients, hospitals and locations along the stent. Consideration of the community composition from individual patients will allow tailoring of prophylactic antibiotic treatments and thus will make the management of stent biofilms more effective.

An in vitro evaluation of hydrolytic enzymes as dental plaque control agents

The plaque-control potential of commercially available amylase, lipase and protease was evaluated by observing their effects on coaggregation and on bacterial viability within various plaque microcosms. A quantitative coaggregation assay indicated that protease significantly inhibited the extent of coaggregation of Actinomyces naeslundii and Streptococcus oralis (P <0.05) and of Porphyromonas gingivalis and S. oralis. Amylase significantly (P <0.05) increased the coaggregation of A. naeslundii versus Fusobacterium nucleatum and A. naeslundii versus P. gingivalis. Concomitant challenge of constant-depth film fermenter-grown plaques with the enzymes did not result in detectable ecological perturbations (assessed by differential culture and denaturing gradient gel electrophoresis). Similar dosing and analysis of multiple Sorbarod devices did not reveal increases in bacterial dispersion which could result from disaggregation of extant plaques. A short-term hydroxyapatite colonization model was therefore used to investigate possible enzyme effects on early-stage plaque development. Whilst culture did not indicate significant reductions in adhesion or plaque accumulation, a vital visual assay revealed significantly increased aggregation frequency following enzyme exposure. In summary, although hydrolytic enzymes negatively influenced binary coaggregation, they did not cause statistically significant changes in bacterial viability within plaque microcosms. In contrast, enzyme exposure increased aggregation within extant plaques.

Fusobacterial infections: clinical spectrum and incidence of invasive disease

OBJECTIVES

Clinically significant infections caused by members of the genus Fusobacterium are rare. We sought to describe the spectrum of clinical disease and epidemiology of these conditions presenting to an acute hospital over a five year period.

METHODS

Clinical records relating to consecutive laboratory isolates of Fusobacterium species were reviewed and cases classified according to pre-specified definitions of primary site and invasive infection.

RESULTS

78 Fusobacterium isolates were identified, 25 of which were associated with invasive disease, most commonly in men (76% of cases). Invasive Fusobacterium necrophorum infection of the head and neck was not observed in patients over 50. Invasive intra-abdominal disease was not observed amongst those under 60. 2 cases of Fusobacterium nucleatum bacteraemia were identified in neutropenic children. One retroperitoneal abscess may have represented secondary infection due to periodontitis. Obstetric infections were the most common clinical syndromes associated with isolates from the female genital tract. The incidence of invasive head and neck disease in the population aged 15-50 was 6.7 per million/year. There were no deaths.

CONCLUSIONS

Invasive fusobacterial infections are rare, affect distinct patient groups and are associated with good clinical outcomes in the majority of cases.

Site-specific development of periodontal disease is associated with increased levels of Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia in subgingival plaque

BACKGROUND

Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia (previously T. forsythensis), which are regarded as the principal periodontopathogenic bacteria, exist as a consortium in subgingival biofilms. We aimed to examine quantitative relationships between P. gingivalis, T. denticola, and T. forsythia in subgingival biofilms and the relationship between the quantity and prevalence of these three bacteria and site-specific periodontal health.

METHODS

This study was cross-sectional. The study population consisted of 35 adult subjects who visited the Kyushu Dental College Hospital. Plaque samples were collected from 105 periodontal pocket sites. Quantitative analyses of each of the three periodontopathogenic bacteria were performed using real-time polymerase chain reaction with species-specific primers and hybridization probes.

RESULTS

The plaque samples were divided into four groups based on the presence or absence of a periodontal pocket (probing depth [PD] > or =4 mm) and bleeding on probing (BOP), regardless of attachment loss. The proportions of all three target bacteria detected in samples from sites of periodontal disease (with PD and BOP) were markedly higher than those in the other sample groups. Cell numbers of P. gingivalis, T. denticola, and T. forsythia in the subgingival plaque of each sampling site were significantly mutually correlated and were increased in the plaque of sites of periodontal disease with PD > or =4 mm and BOP.

CONCLUSION

The symbiotic effects of P. gingivalis, T. denticola, and T. forsythia, which coaggregate and exist concomitantly in subgingival biofilms, may be associated with the local development of periodontitis.